The invention pertains to a color sensor system to identify and synchronize the color panels of an ink ribbon loaded in a thermal printer. The color sensor system can detect any specific color panel and synchronize the first color frame to be printed while wasting as few ribbon frames as possible. More particularly it pertains to a novel panel identification solution for a quicker and more cost effective technology.
In the field of printer technology, a number of different methods have been developed for applying ink to paper, plastic cards or other print media in a controlled manner. One of the most common methods is through the use of ink ribbons. A flexible ribbon-shaped substrate is impregnated or coated with an ink that adheres to paper or a plastic card. The act of printing depletes the print substance so that the substrate must periodically be replaced. The use of replaceable ribbons, supply spools, and take-up spools is therefore common in many different types of printers.
In one type of thermal printer which prints colored images, a carrier contains a repeating series of spaced frames of different colored heat transferable dyes. In such an apparatus, the carrier is disposed between a receiver, such as coated paper, and a print head formed of, for example, a plurality of individual heating elements. When a particular heating element is energized, it is heated and causes dye from the carrier to transfer to the receiver. The density or darkness of the printed color dye is a function of the energy delivered from the heating element to the carrier.
Thermal dye transfer printers offer the advantage of true xe2x80x9ccontinuous tonexe2x80x9d dye density transfer. This result is obtained by varying the energy applied to each heating element, yielding a variable dye density image pixel on the receiver.
The carrier often includes a repeating series of spaced yellow, magenta, and cyan dye frames. The carrier may also include a varnish frame to protect the color from UV rays and protect against abrasion and a black frame.
First, the yellow frame and the receiver are moved until they are positioned under the print head and as they are advanced, the heating elements are selectively energized to form a row of yellow image pixels on the receiver. This process is repeated until a yellow dye image is formed in the receiver. Next, the magenta frame is moved under the print head and the receiver is also moved under the print head. Both the receiver and the magenta frame are moved as the heating elements are selectively energized and a magenta image is formed superimposed upon the yellow image. Finally, as the cyan dye frame and the receiver are moved under the print head, the heating elements are selectively energized and a cyan dye image is formed in the receiver superimposed upon the yellow and magenta dye images. These yellow, magenta and cyan dye images combine to form a colored image.
Since the carrier has a repeating series of yellow, magenta and cyan dye frames, it is important to identify the leading yellow frame of each series (See FIG. 2). One way to identify the leading yellow frame is to employ a conventional sensitometer. The sensitometer identifies a yellow dye frame by producing a particular analog signal in response to light passing through the yellow dye frame. A sensitometer is effective but can be complex and expensive to implement in a printer.
Another way to identify a yellow dye frame is by a code field. A code field is composed of a series of spaced black bars disposed in a clear interframe area between each dye frame. This code field can identify the particular color of the following frame. A reader station can be provided which includes a plurality of photodetectors which are aligned to produce a particular output signal representing the color of the following dye frame. Such a system can perform quite satisfactorily but requires decoding electronics and involves additional manufacturing steps for forming each code field in the clear interframe areas of the carrier.
A third way to identify the color of each dye frame is by using a red light source that provides two logical levels representing only two xe2x80x9ccolorsxe2x80x9d which are: transparent (for yellow, magenta, varnish, etc) and dark (for cyan, black, etc). This solution often requires a wheel with holes and an optical sensor to calculate the distance to move the film to align the yellow frame with the print head.
A fourth way to identify the color of each dye frame is by using both a yellow and a red light source transmitted through each dye frame. The problem with this method is that the method fails to detect a difference between the yellow dye frame and the varnish dye frame and also fails to detect a difference between the cyan dye frame and the black dye frame. The logical levels of this method are as follows:
A fifth way to identify the color of each dye frame is by using a black bar mark located at the beginning of the yellow dye frame. This solution needs an infra-red sensor to detect the black bar mark, a wheel with holes and an optical sensor to calculate the distance to the film must move to synchronize the other dye frames with the print head. This solution represents an expensive technology. What is needed is a cost effective technology that is capable of detecting the actual color of each dye frame without the use of a code system on the ribbon itself or in a clear interframe area between each dye frame.
The invention pertains to a device capable of recognizing any color dye frame from a color ribbon for use in a thermal printer. The device comprises a LED (light emitting diode) capable of producing white light, positioned so that the ribbon passes between the LED and a photo-transistor. The photo-transistor collects the light emitted by the LED as it passes through the color dye frame and generates a specific exit voltage associated with the color of the dye frame. An analog-to-digital converter (ADC) transforms the exit voltage into a digital signal and a micro-computer processes the digital signal and compares the digital signal to a stored set of values associated with each color dye frame.
Because ribbon having color dye frames (panels) is always organized according to a specific sequence, e.g., yellow, magenta, cyan, black, the ribbon can be automatically driven and synchronized so that once the first yellow dye frame is aligned with the print head, all subsequent dye frames will also be aligned with the print head.
The foregoing and additional features and advantages of the present invention will become apparent by way of non-limitative examples shown in the accompanying drawings and the detailed description that follows. In the figures and written description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawings and the written description.